Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 1,589	$ 1,513	$ 1,509	$ 1,453	$ 1,399	$ 1,439	$ 1,482	$ 1,341	$ 6,063	$ 5,661	$ 5,313
Operating profit	628	658	677	648	857	1,348	651	512	2,610	3,369	1,917
Net income	299	452	457	430	569	923	412	323	1,638	2,228	1,268
Net income attributable to S&P Global common shareholders	$ 263	$ 414	$ 421	$ 399	$ 537	$ 892	$ 383	$ 294	$ 1,496	$ 2,106	$ 1,156
Net income:
Basic (in dollars per share)	$ 1.03	$ 1.62	$ 1.63	$ 1.54	$ 2.07	$ 3.39	$ 1.45	$ 1.11	$ 5.84	$ 8.02	$ 4.26
Diluted (in dollars per share)	$ 1.02	$ 1.61	$ 1.62	$ 1.53	$ 2.05	$ 3.36	$ 1.44	$ 1.10	$ 5.78	$ 7.94	$ 4.21
Pre-tax gain (loss) on dispositions	$ 379					$ 722			$ 1,100
Gain (loss) on disposition of business, net of tax	$ 297					$ 521